Power over Ethernet (PoE) refers to a technology in which an Ethernet power-sourcing equipment (PSE) supplies power for a powered device (PD) through an Ethernet cable. The longest distance of reliable power supply of PoE is 100 meters. When the PSE and the PD are a bit far away from each other and a wiring is placed outdoors, the PSE and the PD are very vulnerable to lightening strikes. Therefore, it is necessary to provide protective measures.
The PSE includes a PoE control chip, which outputs a 48 volts direct current voltage through a set of direct current output ends. The set of direct current output ends includes a first direct current output end and a second direct current output end. The voltage between the first direct current output end and the second direct current output end is 48 volts. In the prior art, a port protection circuit is usually added to the PSE. A schematic diagram of a port protection circuit in the prior art is shown in FIG. 1.
An existing port protection circuit mainly includes a differential mode suppression component D1 and a common mode suppression component. An end of the differential mode suppression component D1 is connected to the first direct current output end of the PoE control chip, and the other end of the differential mode suppression component D1 is connected to the second direct current output end of the PoE control chip. The common mode suppression component includes a first voltage dependent resistor RV1 and a second voltage dependent resistor RV2. A first end of the first voltage dependent resistor RV1 is connected to the first direct current output end of the PoE control chip, and the other end of the first voltage dependent resistor RV1 is grounded. A first end of the second voltage dependent resistor RV2 is connected to the second direct current output end of the PoE control chip, and the other end of the second voltage dependent resistor RV2 is grounded.
The existing port protection circuit uses two voltage dependent resistors to protect against a common mode surge. When a common mode surge occurs, a differential mode residual voltage may be caused since it is impossible for the two voltage dependent resistors to act consistently. When the differential mode residual voltage is large, the PoE control chip is damaged.